qwerkus said:
Keep in mind that this type of fuses has a non negligible resistance, which equates more overall power losses. Best way to protect against balancing wire shorts in my opinion is having those wire run ABOVE a kapton layer taped on top of your cells. You than scratch a small piece off wherever you need to solder the end of the balancing wire, keeping the entire wire length insulated from the cells. Should one brake or melt, no risk of shorting another cell. Also a good overall practice is to tape / fasten / glue the wires to reduce possible movement to a minimum in case of failure.
This is kind of what I did. I did actually datalog the difference in cell IR vs a balance cable with none. I found negligible change in resistance in the logs. I did test short circuit breaking action too, they work good and break the circuit if there is any serious potential of wiring being damaged or BMS failure at a catastrophic level. Close to the battery as possible, between the BMS and the cells, there is wire, traveling into no-mans ( where a damage might occur) land, so that wire is fused.
I mean, the bluetooth BMS can instantly tell me if something is wrong before fire when I see one cell group is gone. Never happened for me though. Fact of the matter, a damaged balance harness can absolutly potentially short to another in the BMS harness or pack voltage potential and has enough power to melt the wire and create a fire hazzard.. given high high power and currents these batteries are capable of....and I figured it would be a good idea to protec.
I did test. Parts: 1 DIP switch board, littlefuses, and a few header. Less than a dolla. Each board holds 7 hots and a ground. Im not a EE at all but I did experiment. I wanted to build batteries with very short balance leads and leave the lead on the charger. I dont like JST... at all. They are the weakest link in the entire battery chain... everything else is bolted. Just a dolla in off the shelf component. This way I only have about 1/2 inch of balance lead from the lipo I build... I have used on both hobby charged packs and BMS managed packs.
Plus, if you are not charging wimpy 18650 packs, and are charging high output (say...NMC) cells, you can take advantage of a heavier BMS harness wire (>24g) and higher (>6a) current to balance per cell, something to consider when charging over 2C.... quickly.
In practice, if you short something on the balance wires, the wire itself acts like a fuse and goes open pretty fast. It may or may not start a fire in the process.
....
(but what if you have a big, big, balance wire (>18ga) that can take some serious current and her output before fusing?)
fuses on balance wires is generally a bad thing with the cheap bms used here.
breaking a fuse usually means something went REALLY wrong and will cause a cascading effect with the other balance wires if you are unlucky so the entire bms burns down.
( this stops all high current fault flow.. and the system just reports a dead string... easily monitored.. lol... )
personally i would not protect the balancing circuit and if something happens you need a LOT of power onto a single component so you know for sure it blows up and breaks the short and protects the rest of the batter
... snt this the reason for a "distributed BMS" vs a "non distributed"BMS, and all the advantages that go along with each system? IDK... ?
The board in the corner of the picture would hold 32 balance wires, for 32 cells, with 32 fuses. No current would be catastrophic if the battery would go out of its "safe operation area" and begin to give current into the balance lines over designed spec.
IDK I thought picofuses WERE/ARE PTC type fuses? IDK I might be wrong.
